Magnetic recording system and magnetic recording medium used therefor

ABSTRACT

A magnetic recording system high in S/N and low in bit error rate, capable of carrying out writing and reading of high recording density of at least 1 gigabit per 1 square inch and high in reliability can be realized by making the magnetic layer of the magnetic recording medium from a mixture comprising at least one non-magnetic compound selected from the group consisting of oxides and nitrides and a magnetic material comprising Co and Pt as main components and specifying the molar ratio of Pt to Co in the magnetic layer, and employing a magnetoresistive read back magnetic recording head.

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic recording system used for anauxiliary recording system of computers and the like and a magneticrecording medium used for the magnetic recording system. Moreparticularly, it relates to a magnetic recording system having a highrecording density of 1 gigabit per 1 square inch or more and a magneticrecording medium suitable for realizing the high recording density.

JP-A-5-73880 discloses a magnetic recording medium which comprises aCoCrPt magnetic layer containing silicon oxide, zirconium oxide,tantalum oxide, silicon nitride, boron nitride, titanium nitride oraluminum nitride.

JP-A-5-197944 discloses a magnetic recording medium which comprises aCoNiPtMO magnetic layer or CoCrPtMO magnetic layer (M is at least oneelement selected from Si, B, Zr, Al, Y, P, Ti, Sn and In).

In the above conventional magnetic recording media, coercivity isincreased and medium noise is decreased by adding oxides or nitrides tothe magnetic layer of the media.

However, according to the investigation by the inventors, the aboveconventional magnetic recording media suffer from the problems thatdecrease of medium noise in the high linear recording density area ofhigher than 150 kFCI (Flux Change per Inch) is insufficient and it isdifficult to realize a high recording density of at least 1 gigabit persquare inch.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to solve the abovetechnical problems and to provide a magnetic recording system whichmakes it possible to attain a high recording density of at least 1gigabit per 1 square inch, and a magnetic recording medium suitable forrealizing the high recording density.

In the first aspect, the present invention provides a magnetic recordingsystem having a magnetic recording medium and a magnetic recording headwhich carries out writing in and reading back from the magneticrecording medium, said magnetic recording medium comprising a substrateand a magnetic layer formed on the substrate directly or indirectly withan underlayer intervening between the magnetic layer and the substrate,characterized in that the magnetic layer of the magnetic recordingmedium comprises a mixture of at least one non-magnetic compoundselected from the group consisting of oxides represented by the formulaMOx (wherein M represents at least one element selected from Si, Al, Ta,Y and Ti, and x represents a numerical value of from about 1 to about2.5) and a magnetic material of an alloy comprising Co and Pt as maincomponents, the molar ratio of Pt to Co in the magnetic layer is 0.6-1.2and the molar ratio of the non-magnetic compound to Co is 0.1-2.8, andthe magnetic recording head includes a magnetoresistive read backmagnetic recording head.

In the second aspect, the present invention provides the magneticrecording system having the above construction, characterized in thatthe magneto-resistive read back magnetic recording head has two shieldlayers and a magnetoresistive sensor formed between the shield layersand the distance between the two shield layers is 0.35 μm or less.

In the third aspect, the present invention provides the magneticrecording system having the above construction, characterized in thatthe product (Br•t) of a residual magnetic flux density, Br, measured byapplying a magnetic field in the relative running direction of themagnetic recording head in respect to the magnetic recording medium atthe time of recording and a thickness, t, of the magnetic layer of themagnetic recording medium is 10-100 gauss•micron.

In the fourth aspect, the present invention provides the magneticrecording system having the above construction, characterized in thatthe coercivity of the magnetic recording medium measured by applying amagnetic field in the relative running direction of the magneticrecording head in respect to the magnetic recording medium at the timeof recording is 2.4 kOe or more.

In the fifth aspect, the present invention provides the magneticrecording system having the above construction, characterized in thatthe magnetoresistive read back magnetic recording head has amagnetoresistive sensor which includes a plurality of magnetic layersand non-magnetic layers provided between the magnetic layers, saidmagnetic layers causing a great change in resistivity due to a relativechange of mutual magnetization directions by an external magnetic field.

In the sixth aspect, the present invention provides the above-mentionedmagnetic recording system of the first aspect, characterized in that thenon-magnetic compound in the magnetic layer of the magnetic recordingmedium is not an oxide, but a nitride represented by the formula LNy(wherein L represents at least one element selected from Si, B and Aland y represents a numerical value of from about 1 to about 1.3).

The inventions of the second to fifth aspects can also be applied to theinvention of the sixth aspect.

It is further preferred in the invention of the first or sixth aspectthat the molar ratio of the non-magnetic compound to Co in the magneticlayer of the magnetic recording medium is 0.5-2.4.

In the seventh aspect, the present invention provides a magneticrecording medium comprising a substrate and a magnetic layer formed onthe substrate directly or indirectly with an underlayer interveningbetween the magnetic layer and the substrate, characterized in that themagnetic layer of the magnetic recording medium comprises a mixture ofat least one non-magnetic compound selected from the group consisting ofoxides represented by the formula MOx (wherein M represents at least oneelement selected from Si, Al, Ta, Y and Ti, and x represents a numericalvalue of from about 1 to about 2.5) and a magnetic material of an alloycomprising Co and Pt as main components, the molar ratio of Pt to Co inthe magnetic layer is 0.6-1.2 and the molar ratio of the non-magneticcompound to Co is 0.1-2.8.

In the eighth aspect, the present invention provides the magneticrecording medium of the seventh aspect, characterized in that thenon-magnetic compound in the magnetic layer of the magnetic recordingmedium is not an oxide, but a nitride represented by the formula LNy(wherein L represents at least one element selected from Si, B and Aland y represents a numerical value of from about 1 to about 1.3).

It is further preferred in the invention of the seventh or eighth aspectthat the molar ratio of the non-magnetic compound to Co in the magneticlayer of the magnetic recording medium is 0.5-2.4.

The inventors have prepared various magnetic recording media by changingthe composition of the magnetic layer to search for the composition ofthe magnetic layer which is optimum when the medium is combined with amagnetic recording head. Furthermore, they have changed the magneticrecording heads to search for magnetic recording heads having thestructure which is optimum when the magnetic recording head is combinedwith the magnetic recording medium. As a result, the magnetic recordingsystems and magnetic recording media of the present invention have beenaccomplished.

In the magnetic recording system of the first aspect, the magnetic layerof the magnetic recording medium is composed of a mixture of at leastone non-magnetic compound selected from the group consisting of oxidesand nitrides and a magnetic material of an alloy comprising Co and Pt asmain components, the molar ratio of Pt to Co in the magnetic layer islimited to 0.6-1.2, and, furthermore, a magnetoresistive read backrecording head is employed.

When Co and Pt are used as the main components of the magnetic materialand the molar ratio of them is limited and the magnetic recording mediumis combined with a magnetoresistive head, the medium S/N can beincreased to about 2.0 or more. The medium S/N is a ratio of output tomedium noise (a value obtained by excluding the noise of system from thetotal noise). Thus, the medium noise in a high linear recording densityarea of at least 150 kFCI can be sufficiently reduced, a high recordingdensity of at least 1 gigabit per 1 square inch can be realized, and amagnetic recording system of high reliability with low bit error ratecan be obtained.

When Cr or Ni are added to the CoPt magnetic material, coercivity andcoercivity squareness decrease in the area of high concentration of thenon-magnetic compound and this is not preferred.

Cr, Ni, etc. have the property of readily segregating at the crystalgrain boundary of the Co alloy. In a Co alloy thin film magneticrecording medium containing no non-magnetic compound, the segregation ofCr or Ni at the grain boundary has the effect to lower the exchangeinteraction between the crystal grains and enhance the coercivity.However, in the case of a magnetic recording medium containing thenon-magnetic compound at a high concentration, since the exchangeinteraction between crystal grains is already lowered by thenon-magnetic compound, there is no effect to enhance the coercivity dueto the lowering of the exchange interaction caused by the addition ofCr, Ni and the like, and, furthermore, the elements such as Cr and Nireduce crystal magnetic anisotropy of the CoPt alloy. Therefore, thealloy may consist essentially of Co and Pt.

In the magnetic recording system of the second aspect, when themagnetoresistive head has two shield layers and a magnetoresistivesensor formed between the shield layers, the distance between the twoshield layers is limited to 0.35 μm or less.

This construction results in about 15% or less of jitter anddiscrimination of bits can be satisfactorily made.

In the magnetic recording system of the third aspect, the product ofresidual magnetic flux density, Br, measured by applying a magneticfield in the relative running direction of the magnetic recording headin respect to the magnetic recording medium at the time of recording andthickness, t, of the magnetic layer of the magnetic recording medium(namely, Br•t) is limited to 10-100 gauss•micron.

This results in about 15% or less of jitter and discrimination of bitscan be satisfactorily made.

In the magnetic recording system of the fourth aspect, the coercivity ofthe magnetic recording medium measured by applying a magnetic field inthe relative running direction of the magnetic recording head in respectto the magnetic recording medium at the time of recording is limited to2.4 kOe or more.

When the coercivity is 2.4 kOe or more, system S/N is higher than 1 andthe noise can be made smaller than the signal. The system S/N is a ratioof the output to the noise of the system.

In the magnetic recording system of the fifth aspect, as amagnetoresistive head, there is employed a structure having amagnetoresistive sensor including a plurality of magnetic layers andnon-magnetic layers provided between the magnetic layers, said magneticlayers bringing about a great change in resistivity due to relativechange of mutual magnetization directions caused by an external magneticfield.

According to this construction, signal intensity can be further enhancedby the giant magnetoresistive effect, and a magnetic recording system ofhigh reliability with a recording density of at least 3 gigabits per 1square inch can be realized.

The reason for using an alloy comprising Co and Pt as the maincomponents in a magnetic material of the magnetic layer of the magneticrecording medium is as follows. Hitherto, a (Co+Pt+α) (ternary) alloyhas been used as the magnetic material. However, when an alloycomprising (Co+Pt) as the main components is used while limiting thecompositional ratio thereof and this magnetic material is combined witha magnetoresistive head, the medium S/N can be made to about 2.0 orhigher. Thus, the medium noise in the high linear recording density areaof 150 kFCI or higher can be sufficiently reduced and a high recordingdensity of 1 gigabit or higher per 1 square inch can be realized.

Elements such as Ar which are inevitably taken in during film-forming bysputtering or the like may be contained in a slight amount in themagnetic material.

The reasons for employing an oxide represented by the formula MOx(wherein M represents at least one element selected from Si, Al, Ta, Yand Ti, and x represents a numerical value of from about 1 to about 2.5)as the non-magnetic compound in the magnetic layer of the magneticrecording medium and limiting the molar ratio of the non-magneticcompound to Co in the magnetic layer to 0.1-2.8 are as follows. When themolar ratio of the oxide to Co is 0.1 or more, normalized noise can bereduced to 0.025 or less. The normalized noise is a value obtained bynormalizing with a signal output of 10 kFCI the medium noise when asignal is recorded at a recording density of 150 kFCI. Furthermore, thecoercivity can be increased to 2.4 kOe or more. When the molar ratio ofthe oxide to Co is 2.8 or less, a sufficient output can be obtained.

According to the sixth aspect of the present invention, in the magneticrecording system of the first aspect, a nitride represented by theformula LNy (wherein L represents at least one element selected from Si,B and Al and y represents a numerical value of from about 1 to about1.3) is employed in place of the oxide as the non-magnetic compound inthe magnetic layer of the magnetic recording medium.

When the molar ratio of the nitride to Co is 0.1 or more, normalizednoise can be reduced to 0.025 or less. Moreover, the coercivity can beincreased to 2.4 kOe or more. When the molar ratio of the nitride to Cois 2.8 or less, a sufficient output can be obtained.

The reason for limiting the molar ratio of the non-magnetic compound toCo in the magnetic layer of the magnetic recording medium to 0.5-2.4 isthat when the molar ratio of the non-magnetic compound to Co is limitedto the range of 0.5-2.4, the normalized noise can be reduced to 0.016 orless, and, moreover, the coercivity can be increased to 2.4 kOe or more.

In the magnetic recording medium of the seventh aspect, the magneticlayer is composed of a mixture of at least one non-magnetic compoundselected from the group consisting of oxides represented by the formulaMOx (wherein M represents at least one element selected from Si, Al, Ta,Y and Ti, and x represents a numerical value of from about 1 to about2.5) and an alloy magnetic material comprising Co and Pt as maincomponents, the molar ratio of Pt to Co in the magnetic layer is limitedto 0.6-1.2 and the molar ratio of the non-magnetic compound to Co islimited to 0.1-2.8.

When Co and Pt are used as the main components of the magnetic materialand the molar ratio of them is limited, the medium S/N can be increasedto about 2 or more. Thus, the medium noise in a high linear recordingdensity area of at least 150 kFCI can be sufficiently reduced and a highrecording density of at least 1 gigabit per 1 square inch can berealized.

The reason for using an alloy comprising Co and Pt as main components asa magnetic material of the magnetic layer is as follows. Hitherto, a(Co+Pt+α) (ternary) alloy has been used as the magnetic material.However, when the alloy comprising (Co+Pt) as main components is usedwhile limiting the compositional ratio thereof, the medium S/N can bemade to be about 2.0 or more. Thus, the medium noise in the high linearrecording density area of 150 kFCI or more can be sufficiently reducedand a high recording density of 1 gigabit or more per 1 square inch canbe realized.

The reasons for employing an oxide represented by the formula MOx(wherein M represents at least one element selected from Si, Al, Ta, Yand Ti, and x represents a numerical value of from about 1 to about 2.5)as the non-magnetic compound in the magnetic layer and limiting themolar ratio of the non-magnetic compound to Co in the magnetic layer to0.1-2.8 are as follows. When the molar ratio of the oxide to Co is 0.1or more, normalized noise can be reduced to 0.025 or less. Moreover,coercivity can be increased to 2.4 kOe or more. When the molar ratio ofthe oxide to Co is 2.8 or less, a sufficient output can be obtained.

According to the eighth aspect of the present invention, in the magneticrecording medium of the seventh aspect, a nitride represented by theformula LNy (wherein L represents at least one element selected from Si,B and Al and y represents a numerical value of from about 1 to about1.3) is used in place of the oxide as the non-magnetic compound in themagnetic layer.

When the molar ratio of the nitride to Co is 0.1 or more, normalizednoise can be reduced to 0.025 or less. Moreover, coercivity can beincreased to 2.4 kOe or more. When the molar ratio of the nitride to Cois 2.8 or less, a sufficient output can be obtained.

The reason for limiting the molar ratio of the non-magnetic compound toCo in the magnetic layer to 0.5-2.4 in the invention of the seventh oreighth aspect is that when the molar ratio of the non-magnetic compoundto Co is limited to the range of 0.5-2.4, the normalized noise can bereduced to 0.016 or less and, moreover, coercivity can be increased to2.4 kOe or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic plan view of the magnetic recording system ofExample 1.

FIG. 1(b) is schematic sectional view of the magnetic recording systemshown in FIG. 1(a) taken along line 1--1.

FIG. 2 is an oblique view which shows the structure of magneticrecording head in the magnetic recording system of Example 1.

FIG. 3 is a schematic view which shows the sectional structure of amagnetoresistive sensor of the magnetic recording head in the magneticrecording system of Example 1.

FIG. 4 is an oblique view which shows the structure of the magneticrecording medium in the magnetic recording system of Example 1.

FIG. 5 is a characteristic curve which shows the relation between themolar ratio of Pt to Co in the magnetic layer of the magnetic recordingmedium and the medium S/N of the magnetic recording medium of Example 1.

FIG. 6 is a characteristic curve which shows the relation between themolar ratio of silicon oxide to Co in the magnetic layer of the magneticrecording medium and the normalized noise of the magnetic recordingmedium of Example 1.

FIG. 7 is a characteristic curve which shows the relation between themolar ratio of silicon oxide to Co in the magnetic layer of the magneticrecording medium and the coercivity of the magnetic recording medium ofExample 1.

FIG. 8 is a characteristic curve which shows the relation between thecoercivity and the system S/N.

FIG. 9 is a block diagram of an apparatus for measuring jitter.

FIG. 10 is a characteristic curve which shows the relation between(Br•t) and jitter.

FIG. 11 is a characteristic curve which shows the relation betweenshield distance and jitter.

FIG. 12 is an oblique view which shows the structure of the magneticrecording medium in the magnetic recording system of Example 2.

FIG. 13 is a schematic view which shows the sectional structure of amagnetoresistive sensor of the magnetic recording head in the magneticrecording system of Example 4.

FIG. 14 is an oblique view which shows the structure of the magneticrecording medium in the magnetic recording system of Example 5.

FIG. 15 is an oblique view which shows the structure of the magneticrecording medium in the magnetic recording system of Example 6.

FIG. 16 is a characteristic curve which shows the relation between themolar ratio of silicon oxide to Co in the magnetic layer of the magneticrecording medium and the normalized noise of the magnetic recordingmedium of a Comparative Example.

FIG. 17 is a characteristic curve which shows the relation between themolar ratio of silicon oxide to Co in the magnetic layer of the magneticrecording medium and the coercivity of the magnetic recording medium ofthe Comparative Example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be explained in detail by the followingexamples. These examples do not limit the invention in any manner.

EXAMPLE 1

FIGS. 1(a) and (b) are a schematic plan view and a schematic sectionalview of a magnetic recording system 70 of Example 1.

The magnetic recording system 70 has a magnetic recording medium 71,magnetic recording medium driving unit 72 which rotates the magneticrecording medium 71 in the recording direction, magnetic recording head73 which carries out writing in and reading back from the magneticrecording medium 71, magnetic recording head driving unit 74 whichdrives the magnetic head 73 relatively to the magnetic recording medium71, and read/write signal processing part 75 which carries outprocessing of the write signal or read signal.

FIG. 2 shows the structure of the magnetic recording head 73.

The magnetic recording head 73 is a dual head with an inductive head forwriting and a magnetoresistive (MR) read back recording head. That is,the portion comprising upper recording magnetic pole 86 and shieldlayer-recording magnetic pole 84 which hold coil 85 therebetween acts asa magnetic recording head for writing. The portion comprising the shieldlayer-recording magnetic pole 84 and lower shield layer 83 between whichmagnetoresistive sensor 82 and electrode pattern 87 are held acts as amagnetic recording head for read back. The output signal from themagnetoresistive sensor 82 is taken out through the electrode pattern87. The lower shield layer 83 is formed on slider substrate 81.

FIG. 3 shows a sectional structure of the magnetoresistive sensor 82.

The magnetoresistive sensor 82 is provided on the lower shield layer 83with a gap layer 91 intervening between them, and the magnetoresistivesensor 82 includes antiferromagnetic domain stabilizing layer 92provided on the gap layer 91, thin film magnetoresistive conductivelayer 93 of a ferromagnetic material which is made in a single domain bythe antiferromagnetic domain stabilizing layer 92, non-magnetic layer 95for cutting off the exchange interaction between sensor 94 of the thinfilm magnetoresistive conductive layer 93 and the antiferromagneticdomain stabilizing layer 92, soft magnetic layer 97 for generating abias magnetic field for the sensor 94, and high resistivity layer 96 forcontrolling the current distribution ratio between the soft magneticlayer 97 and the thin film magnetoresistive conductive layer 93.

The magnetic recording head 73 was made in the following manner.

A sintered body mainly composed of aluminum oxide and titanium carbidewas used as slider substrate 81. An Ni--Fe alloy film 1 μm thick wasformed as lower shield layer 83 by a sputtering method.

An aluminum oxide film 100 nm thick was formed as the gap layer 91 by asputtering method. An NiO layer 20 nm thick was formed as theantiferromagnetic domain stabilizing layer 92 by a sputtering method. AnNb layer 2 nm thick was formed as the non-magnetic layer 95 by asputtering method. An Ni--Fe alloy layer 15 nm thick was formed as thethin film magnetoresistive conductive layer 93 by a sputtering method. ATa layer 15 nm thick was formed as the high resistivity layer 96 by asputtering method. An Ni--Fe--Nb alloy layer 20 nm thick was formed asthe soft magnetic layer 97 by a sputtering method.

A Cu thin film 100 nm thick was formed as the electrode pattern 87 by asputtering method.

Gap layer 98 comprising aluminum oxide of 100 nm thickness was formedbetween the electrode pattern 87 and the shield layer-recording magneticpole 84 by a sputtering method.

An Ni--Fe alloy layer 1 μm thick was formed as the soft shieldlayer-recording magnetic pole 84 by a sputtering method.

A Cu film 3 μm thick was formed as coil 85 by a sputtering method.

An Ni--Fe alloy layer 3 μm thick was formed as the upper recordingmagnetic pole 86 by a sputtering method.

A gap layer comprising aluminum oxide 300 nm thick was also formedbetween the shield layer-recording magnetic pole 84 and the upperrecording magnetic pole 86 by a sputtering method.

FIG. 4 shows a sectional structure of the magnetic recording medium 71.

The magnetic recording medium 71 comprises substrate 101 of a chemicallyreinforced glass, magnetic layer 103 of Co--Pt magnetic materialcontaining silicon oxide, protective carbon layer 104, and adsorptiveperfluoroalkyl polyether lubricant layer 105.

The magnetic recording medium 71 was made in the following manner.

Magnetic layer 103 having a thickness of 25 nm and made of a Co--Ptmagnetic material containing silicon oxide was formed on a disk-likeglass substrate 101 of 2.5 inches in diameter and 0.4 mm thick by RFmagnetron sputtering method under the deposition conditions of substratetemperature: room temperature, Ar gas pressure: 15 mTorr and powerdensity: 5 W per 1 cm². Then, protective carbon layer 104 10-30 nm thickwas formed on the magnetic layer 103 by DC magnetron sputtering methodunder the deposition conditions of substrate temperature: 150° C., Argas pressure: 5 mTorr and power density: 3 W per 1 cm². Thereafter,polystyrene particles were electrostatically coated on the surface ofthe protective layer 104, followed by subjecting it to plasma etching of15 nm using the polystyrene particle coat as a mask to form microunevenness on the surface of the protective layer 104. Finally, anadsorptive perfluoroalkyl polyether lubricant layer 105 2-20 nm thickwas formed on the protective layer 104 by a dipping method.

FIG. 5 shows the relation between the molar ratio of Pt to Co in theCo--Pt magnetic material and the medium S/N at a recording density of 1gigabit per 1 square inch. The molar ratio of silicon oxide to Co was0.8.

When the molar ratio of Pt to Co was 0.6-1.2, the medium S/N could be2.0 or more.

FIG. 6 shows the relation between the molar ratio of silicon oxide to Coin the Co--Pt magnetic material and the normalized noise. The molarratio of Pt to Co was about 0.67 (60 at % Co-40 at % Pt).

When the molar ratio of silicon oxide to Co was 0.1-2.8, the normalizednoise could be 0.025 or less. Especially, when the molar ratio ofsilicon oxide to Co was 0.5-2.4, the normalized noise could be 0.016 orless.

FIG. 7 shows the relation between the molar ratio of silicon oxide to Coin the Co--Pt magnetic material and the coercivity. The molar ratio ofPt to Co was about 0.67.

When the molar ratio of silicon oxide to Co was 0.1 or more, thecoercivity could be made to 2.4 kOe or more. Especially, when the molarratio of silicon oxide to Co was 0.5-1.4, a coercivity of 3.0 kOe ormore could be obtained and this is preferred.

As shown in FIG. 8, when the coercivity was less than 2.4 kOe, thesystem S/N was lower than 1 and the noise was greater than the signal.Thus, it is necessary that the coercivity be 2.4 kOe or more.

FIG. 8 is a graph prepared by plotting against each coercivity themaximum system S/N obtained by examining the system S/N using mediadifferent in Br•t.

On the other hand, when the molar ratio of silicon oxide to Co washigher than 2.8, sufficient output was not obtained.

Therefore, the molar ratio of silicon oxide to Co is preferably 0.1-2.8.

As shown in FIG. 9, the read output from magnetic recording head 73 waspulsed by low-pass filter 51, differential circuit 52 and pulsingcircuit 53, the fluctuation of pulse interval, δ, was analyzed by jittermeter 54, and the ratio of standard deviation, σ, of pulse interval, δ,to the average value of the pulse interval, δ, was measured as jitter.

FIG. 10 shows the relation between the product (Br•t) of residualmagnetic flux density, Br, measured by applying a magnetic field in therelative running direction of magnetic recording head 73 in respect tomagnetic recording medium 71 at the time of recording and magnetic layerthickness, t, of the magnetic recording medium 71 and the jitter of theoutput signal when the high density signals of a constant frequency werewritten and read back.

When Br•t was in the range of 10-100 gauss•micron, jitter was less thanabout 15%, and discrimination of bits could be satisfactorily made.

FIG. 11 shows the relation between the distance (shield distance)between the lower shield layer 83 and the shield layer-recordingmagnetic pole 84 and the jitter.

When the shield distance was less than 0.35 μm, jitter was less thanabout 15% and the bits could be satisfactorily discriminated.

The write/read characteristics of magnetic recording system 70 havingmagnetic recording medium 71 in which the molar ratio of Pt to Co inmagnetic layer 103 was 0.67 (60 at % Co-40 at % Pt) and the molar ratioof silicon oxide to Co was about 0.9 were evaluated under the conditionsof head flying height: 30 nm, linear recording density: 210 kBPI, andtrack density: 9.6 kTPI.

As a result, the system S/N was 1.8. This value was higher by about 30%than that obtained when 73 at % Co-15 at % Cr-12 at % Pt was used inplace of 60 at % Co-40 at % Pt as the magnetic material.

Moreover, information of 2 gigabits per 1 square inch could be writtenand read by subjecting the input signal into the magnetic recording head73 to 8-9 code modulation processing and subjecting the output signal tomaximum likelihood decoding processing.

The number of bit errors after conducting a head seek test of 50,000times from the inner periphery to the outer periphery was less than 10bits/face and a mean time between failures MTBF of 150,000 hours couldbe attained.

A permanent magnet film bias layer may be used in place of the softmagnetic layer 97 of the magnetoresistive sensor 82.

Ti, Si, Si--C, carbon, crystallized glass, ceramics, etc. may be used asthe material of substrate 101 of the magnetic recording medium 71.

As the material of protective layer 104 of the magnetic recording medium71, there may be used carbides such as tungsten carbide and (W--Mo)--C,nitrides such as (Zr--Nb)--N and silicon nitride, oxides such as silicondioxide and zirconia, and, furthermore, boron, boron carbide, molybdenumdisulfide, Rh, etc. It is preferred to provide the protective layer 104and the lubricant layer 105 because sliding resistance and corrosionresistance can be improved.

Furthermore, when micro unevenness is formed on the surface of theprotective layer 104 by plasma etching using a fine mask or the like, orheterogeneous projections are produced on the surface of the protectivelayer using a target of a compound or mixture, or unevenness is formedon the surface by heat treatment, contact the area between the magneticrecording head 73 and the magnetic recording medium 71 can be reducedand the problem of the magnetic recording head 73 adhering to thesurface of the magnetic recording medium 71 at the time of CSS (contactstart stop) operation can be avoided.

EXAMPLE 2

Magnetic recording medium 71a having the structure shown in FIG. 12 wasused in the magnetic recording system having the same construction as ofExample 1.

This magnetic recording medium 71a had the same structure as that of themagnetic recording medium 71 of Example 1, except that underlayer 121was additionally provided and the material of the magnetic layer 103 waschanged.

The underlayer 121 was formed in the following manner.

Underlayer 121 of Cr having a thickness of 15 nm was formed on adisk-like glass substrate 101 of 2.5 inches in diameter and 0.4 mm inthickness by DC magnetron sputtering method under the depositionconditions of substrate temperature: room temperature, Ar gas pressure:5 mTorr and power density: 7 W per 1 cm².

Ti, V, Ge, Zr, Nb, Mo, Ta, W, and Ni--P may be used as the material ofunderlayer 121.

The material of magnetic layer 103 was 52 at % Co-48 at % Pt to whichsilicon oxide, aluminum oxide, tantalum oxide, yttrium oxide or titaniumoxide was added.

Table 1 shows composition of the magnetic recording medium 71a, magneticproperties and normalized noise. As a comparative example, resultsobtained when 73 at % Co-15 at % Cr-12 at % Pt was used in place of 52at % Co-48 at % Pt are also shown in Table 1.

In all of the magnetic recording media 71a of Example 2, high coercivityand low normalized noise were obtained.

On the other hand, the coercivity was low and the normalized noise washigh in the comparative example where 73 at % Co-15 at % Cr-12 at % Ptwas used.

The write/read characteristics of a magnetic recording system havingmagnetic recording medium 71a of Sample No. 14 shown in Table 1 wereevaluated under the conditions of head flying height: 26 nm, linearrecording density: 210 kBPI, and track density: 9.6 kTPI.

As a result, the system S/N was 1.8.

Moreover, information of 2 gigabits per 1 square inch could be writtenand read by subjecting the input signals into the magnetic recordinghead 73 to 8-9 code modulation processing and subjecting the outputsignals to maximum likelihood decoding processing.

The number of bit errors after conducting a head seek test of 50,000times from the inner periphery to the outer periphery was less than 10bits/face and a mean time between failures MTBF of 150,000 hours couldbe attained.

In the conventional magnetic recording medium, the underlayer isprovided for controlling orientation of the magnetic layer while in themagnetic recording medium of the present invention, it is provided forcontrolling crystal grain size and improvement of adhesion to thesubstrate and corrosion resistance.

                                      TABLE 1    __________________________________________________________________________                       Pt/Co                           MOx/Co      Normalized    Sample          Magnetic     Molar                           Molar                                Hc Br·t                                       noise    No.   material                 Oxide ratio                           ratio                                (kOe)                                   (Gμm)                                       (μVrms/μVpp)    __________________________________________________________________________    11    Co-48 at % Pt                 Silicon                       0.92                           1.05 3.08                                   87  0.013                 oxide    12    Co-48 at % Pt                 Aluminum                       0.92                           1.01 2.83                                   91  0.015                 oxide    13    Co-48 at % Pt                 Tantalium                       0.92                           1.07 2.72                                   84  0.016                 oxide    14    Co-48 at % Pt                 Yttrium                       0.92                           1.01 2.68                                   83  0.017                 oxide    15    Co-48 at % Pt                 Titanium                       0.92                           1.03 2.92                                   89  0.014                 oxide    Comparative          Co-15 at % Cr                 Silicon                       0.16                           1.05 2.05                                   88  0.021    Sample    12 at % Pt          oxide    __________________________________________________________________________

EXAMPLE 3

Silicon nitride, boron nitride or aluminum nitride was added in place ofthe oxide as the non-magnetic compound to the magnetic layer of themagnetic recording medium 71a in Example 2.

Table 2 shows the composition of the magnetic recording medium, magneticproperties and normalized noise. As a comparative example, resultsobtained when 73 at % Co-15 at % Cr-12 at % Pt was used in place of 52at % Co-48 at % Pt are also shown in Table 2.

In all of the magnetic recording media of Example 3, high coercivity andlow normalized noise were obtained.

On the other hand, the coercivity was low and the normalized noise washigh in the comparative example where 73 at % Co-15 at % Cr-12 at % Ptwas used.

The write/read characteristics of the magnetic recording system havingthe magnetic recording medium of Sample No. 21 shown in Table 2 wereevaluated under the conditions of head flying height: 26 nm, linearrecording density: 210 kBPI, and track density: 9.6 kTPI.

As a result, the system S/N was 1.8.

Moreover, information of 2 gigabits per 1 square inch could be writtenand read by subjecting the input signal into the magnetic recording head73 to 8-9 code modulation processing and subjecting the output signal tomaximum likelihood decoding processing.

The number of bit errors after conducting a head seek test of 50,000times from the inner periphery to the outer periphery was less than 10bits/face and a mean time between failures MTBF of 150,000 hours couldbe attained.

                                      TABLE 2    __________________________________________________________________________                       Pt/Co                           LNy/Co      Normalized    Sample          Magnetic     Molar                           Molar                                Hc Br·t                                       noise    No.   material                 Nitride                       ratio                           ratio                                (kOe)                                   (Gμm)                                       (μVrms/μVpp)    __________________________________________________________________________    21    Co-48 at % Pt                 Silicon                       0.92                           1.03 2.91                                   86  0.014                 nitride    22    Co-48 at % Pt                 Boron 0.92                           1.01 2.86                                   89  0.015                 nitride    23    Co-48 at % Pt                 Aluminum                       0.92                           1.05 2.72                                   91  0.017                 nitride    Comparative          Co-15 at % Cr                 Silicon                       0.16                           1.01 1.86                                   87  0.024    Sample    12 at % Pt          nitride    __________________________________________________________________________

EXAMPLE 4

In the magnetic recording system having the same construction as ofExample 1, magnetoresistive sensor 82a shown in FIG. 13 was used inplace of the magnetoresistive sensor 82 (FIG. 3) of the magneticrecording head for reading. Moreover, an Fe--Co--Ni alloy film formed byplating method was used as the upper recording magnetic pole 86 of themagnetic recording head for writing. In addition, the magnetic recordingmedium was changed.

The magnetoresistive sensor 82a shown in FIG. 13 was a magnetoresistivesensor which utilizes resistivity change occurring due to the change inthe relative magnetization directions between the two magnetic layers132 and 134 which are separated by a non-magnetic layer 133(magnetoresistivity change due to the spin valve effect).

Buffer layer 131 was a Ti layer 2 nm thick. The first magnetic layer 132was a 80 at % Ni-20 20 at % Fe alloy layer 3 nm thick. The non-magneticlayer 133 was a Cu layer of 1.5 nm thick. The second magnetic layer 134was a 80 at % Ni-20 at % Fe alloy layer 3 nm thick. Antiferromagneticlayer 135 was a 50 at % Fe-50 at % Mn alloy layer of 5 nm thick.

These layers were all formed by a sputtering method.

In this magnetoresistive sensor 82a, the magnetization of the secondmagnetic layer 134 is fixed in one direction by the exchange biasmagnetic field from the antiferromagnetic layer 135 and themagnetization direction of the first magnetic layer 132 changed by theleakage field from the magnetic recording medium 71 to cause a change inresistivity.

By using Ti as the buffer layer 131, the crystal lattice plane {111} ofthe first magnetic layer 132 and the second magnetic layer 134 wasorientated so that the plane was in parallel to the film surface. Thus,the exchange interaction between the magnetic layers 132 and 134 wasweakened and a sensitivity which was about twice that of themagnetoresistive sensor 82 of Example 1 was obtained.

Furthermore, by using an Fe--Co--Ni alloy film formed by a platingmethod as the upper recording magnetic pole 86, the saturated magneticflux density increased to 16000 gauss and the over writingcharacteristics could be improved by about 6 dB as compared with thoseof Example 3.

The magnetic recording medium had the structure obtained by forming themagnetic layer 103 of 25 nm composed of 52 at % Co-48 at % Pt containingsilicon oxide at a molar ratio of 1.2 (molar ratio of the silicon oxideto Co) on a carbon substrate having a diameter of 1.3 inch, a thicknessof 0.4 mm and a surface roughness of 1 nm under the same conditions asin Example 1, forming thereon protective carbon layer 104 20 nm thick,subjecting the surface to electrostatic coating with polystyreneparticles, carrying out plasma etching of 13 nm using the coat as a maskto form micro unevenness on the surface of the protective layer 104,and, finally, forming an adsorptive perfluoroalkyl polyether lubricantlayer 105 on the protective layer 104 by a dipping method.

The coercivity measured by applying a magnetic field in thecircumferential direction of the disk of this magnetic recording mediumwas 2.71 kOe and the product of residual magnetic flux density, Br, andthe total magnetic layer thickness, t, (Br•t) was 62 gauss•micron.

The write/read characteristics of the magnetic recording system ofExample 4 were evaluated under the conditions of head flying height: 25nm, linear recording density: 260 kBPI, and track density: 11.6 kTPI.

As a result, the system S/N was 1.5.

Information of 3 gigabits per 1 square inch could be written and readback by subjecting the input signal into the magnetic recording head 73to 8-9 code modulation processing and subjecting the output signal tomaximum likelihood decode processing.

The number of bit errors after conducting a head seek test of 50,000times from the inner periphery to the outer periphery was less than 10bits/face and a mean time between failures (MTBF) of 150,000 hours couldbe attained.

The thickness of the non-magnetic layer 133 in the magnetoresistivesensor 82a is preferably 1.5 nm or more, but if it is too thick, theover writing characteristics are deteriorated since the distance betweenthe magnetic recording head for writing and the lowermost magnetic layer132 is great. Especially, when the non-magnetic layer has a two-layerstructure, the over writing characteristics are deteriorated because thenon-magnetic layer becomes too thick. In order to solve this problem, itis effective to use as the recording magnetic pole of the magneticrecording head for writing a soft magnetic thin film of an Fe--Co--Nialloy, an Fe--Si alloy or the like which has a higher saturated magneticflux density than the conventional Ni--Fe alloys. Especially, goodresults can be obtained when a soft magnetic thin film having asaturated magnetic flux density of at least 15000 gauss is used.

EXAMPLE 5

As shown by magnetic recording medium 71b in FIG. 14, the medium mayhave a structure comprising a substrate 101 of Al--Mg alloy and, formedon both sides thereof, non-magnetic plated layer 102 of Ni--P, Ni--W13 Por the like, magnetic layer 103, protective layer 104 and lubricantlayer 105.

EXAMPLE 6

As shown by magnetic recording medium 71c in FIG. 15, the medium mayhave a structure comprising a substrate 101 of Al--Mg alloy and, formedon both sides thereof, non-magnetic plated layer 102 of Ni--P, Ni--W--Por the like, underlayer 121, magnetic layer 103, protective layer 104and lubricant layer 105.

COMPARATIVE EXAMPLE 1

Relations between the molar ratio of silicon oxide to Co and thenormalized noise and between the molar ratio of silicon oxide to Co andthe coercivity (Hc) when 73 at % Co-15 at % Cr-12 at % Pt was used asthe magnetic material of the magnetic layer 103 of the magneticrecording medium 71 of Example 1 were examined.

As shown by a line joining filled data points in FIG. 16, when the molarratio of silicon oxide to Co was more than 0.1, the normalized noise wasgreater than that of the magnetic recording medium 71 of Example 1 shownby a line joining unfilled data points.

Furthermore, as shown by a line joining filled data points in FIG. 17,when the molar ratio of silicon oxide to Co was more than 0.2, thecoercivity was lower than that of the magnetic recording medium 71 ofExample 1 shown by a line joining unfilled data points.

COMPARATIVE EXAMPLE 2

In place of adding the oxide or nitride, a mixed gas comprising an Ar.sputtering gas used for film deposition by sputtering and oxygen ornitrogen was used.

The coercivity was increased to some extent. However, the effect ofreducing the normalized noise was small and it was difficult to realizea recording density of higher than 1 gigabit per 1 square inch.

It is considered that this is because when an oxygen or nitrogen mixedgas is used, oxygen or nitrogen is taken into not only crystal grainboundary, but also crystal grains and this damages the crystallinity.

According to the magnetic recording system and the magnetic recordingmedium of the present invention, a high S/N and a low bit error rate canbe obtained, and, therefore, a mean time between failures of more than150,000 hours can be realized with a high recording density of at least1 gigabit per 1 square inch.

What is claimed is:
 1. A magnetic recording system having a magneticrecording medium and a magnetic recording head, said magnetic recordingmedium comprising a substrate and a magnetic layer formed on thesubstrate directly or indirectly with an underlayer intervening betweenthe magnetic layer and the substrate and said magnetic recording headcarrying out writing in and reading back from the magnetic recordingmedium, wherein the magnetic layer of the magnetic recording mediumconsists essentially of a mixture of at least one non-magnetic compoundselected from the group consisting of oxides represented by the formulaMOx (wherein N represents at least one element selected from the groupconsisting of Si, Al, Ta, Y and Ti, and x represents a numerical valueof from about 1 to about 2.5) and a magnetic material of an alloyconsisting essentially of Co and Pt, wherein the molar ratio of Pt to Coin the magnetic layer falls within the range of from 0.6 to 1.2, andwherein the molar ratio of the non-magnetic compound to Co falls withinthe range of from 0.1 to 2.8, and the magnetic recording head includes amagnetoresistive read back magnetic recording head.
 2. The magneticrecording system according to claim 1, wherein the magnetoresistive readback magnetic recording head has two shield layers and amagnetoresistive sensor formed between the shield layers and thedistance between the two shield layers is 0.35 μm or less.
 3. Themagnetic recording system according to claim 1, wherein the product(Br•t) of a residual magnetic flux density, Br, measured by applying amagnetic field in the relative running direction of the magneticrecording head in respect to the magnetic recording medium at the timeof recording and a thickness, t, of the magnetic layer of the magneticrecording medium falls within the range of from 10 to 100 gauss•micron.4. The magnetic recording system according to claim 1, wherein thecoercivity of the magnetic recording medium measured by applying amagnetic field in the relative running direction of the magneticrecording head in respect to the magnetic recording medium at the timeof recording is 2.4 kOe or more.
 5. The magnetic recording systemaccording to claim 1, wherein the magnetoresistive read back magneticrecording head has a magnetoresistive sensor including a plurality ofmagnetic layers and non-magnetic layers provided between the magneticlayers, said magnetic layers causing a great change in resistivity dueto relative change of mutual magnetization directions by externalmagnetic field.
 6. The magnetic recording system according to claim 1,wherein the molar ratio of the non-magnetic compound to Co in themagnetic layer of the magnetic recording medium falls within the rangeof from 0.5 to 2.4.
 7. A magnetic recording system having a magneticrecording medium and a magnetic recording head, said magnetic recordingmedium comprising a substrate and a magnetic layer formed on thesubstrate directly or indirectly with an underlayer intervening betweenthe magnetic layer and the substrate and said magnetic recording headcarrying out writing in and reading back from the magnetic recordingmedium, wherein the magnetic layer of the magnetic recording mediumconsists essentially of a mixture of at least one non-magnetic compoundselected from the group consisting of nitrides represented by theformula LNy (wherein L represents at least one element selected from thegroup consisting of Si, B and Al and y represents a numerical value offrom about 1 to about 1.3) and a magnetic material of an alloyconsisting essentially of Co and Pt, wherein the polar ratio of Pt to Coin the magnetic layer falls within the range of from 0.6 to 1.2, andwherein the solar ratio of the non-magnetic compound to Co falls withinthe range of from 0.1 to 2.8, and the magnetic recording head includes amagnetoresistive read back magnetic recording head.
 8. The magneticrecording system according to claim 6, wherein the magnetoresistive readback magnetic recording head has two shield layers and amagnetoresistive sensor formed between the shield layers and thedistance between the two shield layers is 0.35 μm or less.
 9. Themagnetic recording system according to claim 7, wherein the product(Br•t) of a residual magnetic flux density, Br, measured by applying amagnetic field in the relative running direction of the magneticrecording head in respect to the magnetic recording medium at the timeof recording and a thickness, t, of the magnetic layer of the magneticrecording medium falls within the range of from 10 to 100 gauss•micron.10. The magnetic recording system according to claim 7, wherein thecoercivity of the magnetic recording medium measured by applying amagnetic field in the relative running direction of the magneticrecording head in respect to the magnetic recording medium at the timeof recording is 2.4 kOe or more.
 11. The magnetic recording systemaccording to claim 7, wherein the magnetoresistive read back magneticrecording head has a magnetoresistive sensor including a plurality ofmagnetic layers and nonmagnetic layers provided between the magneticlayers, said magnetic layers causing a great change in resistivity dueto relative change of mutual magnetization directions by externalmagnetic field.
 12. The magnetic recording system according to claim 7,wherein the molar ratio of the non-magnetic compound to Co in themagnetic layer of the magnetic recording medium falls within the rangeof from 0.5 to 2.4.
 13. A magnetic recording medium comprising asubstrate and a magnetic layer formed on the substrate directly orindirectly with an underlayer intervening between the magnetic layer andthe substrate, wherein the magnetic layer consists essentially of amixture of at least one non-magnetic compound selected from the groupconsisting of oxides represented by the formula MOx (wherein Mrepresents at least one element selected from the group consisting ofSi, Al, Ta, Y and Ti, and x represents a numerical value of from about 1to about 2.5) and a magnetic material of an alloy consisting essentiallyof Co and Pt, wherein the molar ratio of Pt to Co in the magnetic layerfalls within the range of from 0.6 to 1.2, and wherein and the molarratio of the non-magnetic compound to Co falls within the range of from0.1 to 2.8.
 14. The magnetic recording medium according to claim 13,wherein the molar ratio of the non-magnetic compound to Co in themagnetic layer falls within the range of from 0.5 to 2.4.
 15. A magneticrecording medium comprising a substrate and a magnetic layer formed onthe substrate directly or indirectly with an underlayer interveningbetween the substrate and the magnetic layer, wherein the magnetic layerconsists essentially of a mixture of at least one non-magnetic compoundselected from the group consisting of nitrides represented by theformula LNy (wherein L represents at least one element selected from thegroup consisting of Si, B and Al and y represents a numerical value offrom about 1 to about 1.3) and a magnetic material of an alloyconsisting essentially of Co and Pt, wherein the molar ratio of Pt to Coin the magnetic layer falls within the range of from 0.6 to 1.2, andwherein the molar ratio of the non-magnetic compound to Co falls withinthe range of from 0.1 to 2.8.
 16. The magnetic recording mediumaccording to claim 15, wherein the molar ratio of the non-magneticcompound to Co in the magnetic layer falls within the range of from 0.5to 2.4.